A high-efficiency dual-polarized array antenna with stable beam tilt angle

Abstract

This invention discloses a high-efficiency dual-polarized array antenna with stable beam tilt angle, belonging to the field of antenna engineering technology. To eliminate the requirement for an additional phase-shifting feed layer, four novel array elements with phase-shifting capabilities are introduced. By combining two different feed baluns (Marchand balun and direct-feed balun) and two different dipoles (traditional and novel dipoles) in pairs, and by rotating the feed balun by 180°, four relative phase states of 0°, -90°, -180°, and -270° are achieved. Good impedance matching and a stable beam of 23 degrees are achieved in the 3.35GHz-3.9GHz range. The in-band reflection coefficient is less than -10dB, the beam tilt angle change is less than 1 degree, and the overall efficiency at the center frequency reaches 94.3%. The proposed array antenna has advantages such as integration, high efficiency, stable beam, and low cost, and can be better applied in various scenarios such as base stations.

Description

Technical Field

[0001] This invention belongs to the field of antenna engineering technology, specifically relating to a high-efficiency dual-polarized array antenna with stable beam tilt angle. Background Technology

[0002] With the rapid development of modern communication systems, the requirements for array antenna beams are becoming increasingly stringent. For example, to reduce signal interference between cells and increase the received signal of mobile devices, base station antennas often require a fixed beam tilt. Traditional array antennas typically use phase shifters to achieve beam tilt. For instance, in the paper "Dual-polarized spline-loop antenna array with tilt angle radiation for 5G base stations," a 10-degree beam tilt was achieved using a four-part phase shifter, but the excessively long transmission line resulted in significant losses, and the overall antenna efficiency was only 50%. In the paper "A ±45° dual-polarized dual-beam series-fed metasurface antenna array with stable beam angle," a novel series-fed metasurface array antenna achieved a 27-degree beam tilt with an in-band beam angle ripple of 6.5 degrees. Summary of the Invention

[0003] Building upon prior art, this invention proposes a novel method for achieving a high-efficiency dual-polarized tilted beam antenna array with a stable beam angle. To eliminate the requirement for an additional phase-shifting feed layer, four novel array elements with phase-shifting capabilities are introduced. By combining two different feed baluns (Marchand balun and direct-feed balun) and two different dipoles (traditional and novel dipoles) in pairs, and rotating the feed balun by 180°, four relative phase states of 0°, -90°, -180°, and -270° are achieved. Excellent impedance matching and a stable beam angle of 23 degrees are achieved in the 3.35GHz-3.9GHz range. The in-band reflection coefficient is less than -10dB, the beam tilt angle variation is less than 1 degree, and the overall efficiency at the center frequency reaches 94.3%. The proposed array antenna offers advantages such as integration, high efficiency, beam stability, and low cost, making it more suitable for applications in various scenarios, including base stations.

[0004] The technical solution adopted in this invention is as follows:

[0005] A high-efficiency dual-polarized array antenna with stable beam tilt angle is disclosed. The array antenna consists of four equally spaced different elements disposed on a metal floor. Each element consists of two parts: a planar dipole and a vertical feed balun. The four elements are arranged in the following order: first element, second element, third element, and fourth element. The dipole structures of the first and second elements are the same, the dipole structures of the third and fourth elements are the same, the feed balun structures of the first and third elements are the same, and they are 180 degrees out of phase. The feed baluns of the second and fourth elements are also 180 degrees out of phase.

[0006] All dipoles are printed on a single PCB board with four identical square-shaped ring structures. The four ring structures form a square-shaped dipole. The feeding balun consists of two PCB boards with the same feeding structure printed on them. The two PCB boards are intersected to form a cross-shaped structure, which corresponds to the four ring structures of the dipole. The feeding balun feeds the dipole from the corner of the ring structure located at the center of the dipole.

[0007] Furthermore, each ring structure in the dipoles of the first and second units has a square outer shape and an internal shape, and the outer and inner corners of the square ring located at the center of the dipole are chamfered.

[0008] Furthermore, the outer shape of each ring structure in the dipole of the third and fourth units is a square; the internal shape is based on the square, with a rectangular branch extending from the midpoint of each side to the center of the square, the ends of each branch not touching, and a square branch added from each interior corner of the square; so that the interior of each ring structure is divided into five hollow areas: four hollow areas at the four corners and one hollow area in the center. The hollow areas at the four corners are axially symmetric "L-shaped", and the hollow area in the center is a square. The four corners of the hollow area in the center square are connected to the corresponding hollow areas at the four corners.

[0009] Furthermore, in the first unit, the PCB board of one of the power supply baluns has metal sheets printed on both sides. The back side is printed with two vertical strips, one of which is "L" shaped. The top of the two vertical strips is provided with rectangular protrusions to connect the corresponding dipole ring structure. The metal sheet on the front side starts from the bottom section of the PCB board, extends upwards for a while, then bends 90 degrees to the right, then bends 90 degrees upwards again, along the projection area of ​​the "L" shaped metal sheet on the back side to the top, then bends 90 degrees to the right again, extending to the projection area of ​​another metal sheet printed on the back side. The metal sheet on the front side then bends downwards by 90 degrees, and the length of the branch that bends downwards by 90 degrees is less than half the length of the corresponding metal sheet on the back side.

[0010] Furthermore, in the second unit's power supply balun, one of the PCB boards has metal sheets printed on both sides, and two metal sheets are printed on the back. One of them starts from the bottom of the PCB board, first as a horizontal rectangular sheet, then bends upwards at 90 degrees, passes through the middle of the PCB board, and then bends to the right at 90 degrees. A rectangular protrusion is set above the end, which connects to the corresponding dipole. The other sheet includes two areas, a vertical area and a horizontal area, forming a "T" shape. The bottom of the vertical area does not exceed the middle of the PCB board, and the end of the horizontal area corresponds to the end of the first sheet on the back. The metal sheet printed on the front starts from the bottom of the PCB board, in the projection area of ​​the first metal sheet on the back, first extends upwards for a while, then bends to the right at 90 degrees, then bends upwards at 90 degrees, along the projection area of ​​the back metal sheet to the top, then bends to the right at 90 degrees, extending to the projection area of ​​the other metal sheet printed on the back, and then splits into two paths extending upwards and downwards respectively. The branches extending upwards connect to the corresponding dipole ring structure.

[0011] Furthermore, the structure of the power supply balun of the fourth unit is based on the power supply balun of the second unit, with an additional horizontal branch. The horizontal branch is located in the middle of the PCB board with the vertical metal sheet on the front, and the extension direction is inward.

[0012] The array antenna of this invention consists of four equally spaced antenna elements with phase-shifting capabilities. Four relative phase states—0°, -90°, -180°, and -270°—are achieved by designing different feed baluns and rotating them by 180°. Similarly, by designing different dipole shapes, the relative phase and its corresponding group delay can be changed to achieve in-band beam angle stability. Both the antenna layer and the baluns are manufactured using PCB board technology, making them easy to process and structurally stable. Attached Figure Description

[0013] Figure 1 This is a 3D view of a one-dimensional linear array.

[0014] Figure 2 The diagram shows the structure of four phase-shifting antennas.

[0015] Figure 3 A schematic diagram of a traditional array for achieving tilted beams.

[0016] Figure 4 The present invention presents an array schematic diagram to realize tilted beams.

[0017] Figure 5 To correspond the far-field radiation phase to the array elements in order to achieve a stable tilted beam.

[0018] Figure 6 These are schematic diagrams of the design principles for four phase-shifting antennas.

[0019] Figure 7 The image shows the reflection coefficient results for each port of the array.

[0020] Figure 8 This is a diagram showing the isolation results for each port of the array.

[0021] Figure 9 The phase distributions for four phase-shifting antennas are simulated, as well as the phase distributions required to achieve stable beam tilt.

[0022] Figure 10 This shows the radiation patterns of a one-dimensional linear array at different frequencies.

[0023] Figure 11 The transmission phases corresponding to different baluns.

[0024] Figure 12 The effect of rotating the feed balun by 180 degrees on the far-field radiation phase.

[0025] Figure 13 The effect of different antenna shapes on the far-field radiation phase.

[0026] Figure 14 The total efficiency of the one-dimensional linear array and the beam angle as a function of frequency are given. Detailed Implementation

[0027] The array antenna in this embodiment operates in the 3.35-3.9 GHz range. A 3D view of its one-dimensional array structure and structural diagrams of each antenna element are shown below. Figure 1 , Figure 2 The array size of the one-dimensional linear array is 260mm*80mm*18mm. Figure 1 Structures 1, 2, 3, and 4 are four phase-shifting antennas, corresponding to phase distributions of 0°, -90°, -180°, and -270°, respectively. Structure 5 is the metal ground plane for the array antenna. The four antennas are printed on a dielectric substrate 6, F4BM-220, with a thickness of 0.5mm and a dielectric constant of 2.2. Figure 1 As shown, structure 7 indicates that each antenna is fed by two orthogonally placed baluns, with the two baluns having complementary cutouts for cross-placement. Furthermore, structures 8 and 9 indicate that the feeding baluns corresponding to antennas 1 and 2 are rotated 180 degrees and then applied to antennas 3 and 4, respectively.

[0028] The array unit in this embodiment can be divided into two parts: the traditional dipole 1 and dipole 2, and the novel dipole 3 and dipole 4. The dimensions of these four dipoles are all between 28mm*28mm and 30mm*30mm. For the same two-port transmission network, when the port impedance changes, the corresponding transmission phase also changes. The two proposed antenna structures are significantly different, and their corresponding radiation impedances are also different; for example, a sawtooth pattern is added to the novel dipole. Therefore, antennas 1 and 3, which both use a Marchand balun, will exhibit different far-field radiation phases.

[0029] The feeding baluns in this embodiment are also different, and can be divided into two types: Marchand baluns (10 and 11) and direct-feed baluns (12 and 13). All four baluns have a height of 18mm and a lateral dimension between 12.8mm and 14.5mm. Because the equivalent circuits of the two types of baluns are different, they can produce a large transmission phase difference. Figure 2 As shown, different open-circuit stubs were added for different baluns, which effectively achieve the required broadband transmission phase difference. Open-circuit stub 14 measures 2.8mm x 6.2mm; open-circuit stub 15 measures 1.2mm x 3.6mm; open-circuit stub 16 measures 2.5mm x 5.7mm; open-circuit stub 17 measures 1.2mm x 3.2mm; and open-circuit stub 18 measures 3.0mm x 2.0mm. Furthermore, the feed balun 12 of antenna 3 is derived from the feed balun 10 of antenna 1 by rotating it 180 degrees, i.e., the feed point changes from AA' to CC'.

[0030] The embodiment provides a schematic diagram of an array for implementing tilted beams, such as... Figure 3 The diagram shows the traditional implementation of an array, which involves feeding equally spaced array antennas through a phase-shifting feed network layer to achieve a tilted beam. Adding this extra feed network layer increases cost, increases losses, and makes the array antenna's feed network arrangement more complex. Figure 4 This invention proposes a novel method for achieving beam tilting, which integrates phase shift capability into the antenna to achieve tilted beams. This method offers advantages such as high efficiency, integration, and low cost.

[0031] The embodiments provide the far-field radiation phase corresponding to the array elements to achieve a stable tilted beam, such as... Figure 5 As shown. According to the principle of array antennas, in order to achieve stable beam tilt, the far-field radiation phase of the corresponding array element will also change. For example... Figure 5 As shown, the group delay of the antenna increases with the increase of phase shift. Therefore, in order to achieve a stable tilted beam, it is necessary not only to implement four phase shifts, but also to implement different group delays.

[0032] The embodiments provide design schematics for four phase-shifting antennas, such as... Figure 6 As shown, the proposed array antenna consists of two types of baluns and two types of antennas. The phase difference between the two baluns is 90°, and a 180° rotation of the baluns during feeding will produce a 180° phase difference. Furthermore, the group delay of the Marchand balun is greater than that of the direct-fed balun; the group delay of the novel dipole is greater than that of the traditional one. Therefore, by pairing the two antennas according to the schematic diagram, four different antennas with phase shift capability and group delay increasing with phase shift can be obtained.

[0033] The embodiment provides a graph showing the reflection coefficient results for each port of the array, such as... Figure 7 As shown, within the 3.35-3.9GHz range, the reflection coefficient of all ports is less than -10dB, indicating good impedance matching throughout the entire operating bandwidth.

[0034] The embodiment provides an isolation result diagram for each port of the array, such as... Figure 8 As shown, the isolation between different polarizations of the four antennas is close to 20dB within the band, and the isolation between antennas with the same polarization is also greater than 15dB within the band.

[0035] The examples provide simulated phase distributions for four phase-shifting antennas, as well as the phase distributions required to achieve stable beam tilt. For example... Figure 9 As shown. According to the array principle of a one-dimensional linear array, in order to achieve a stable beam, the phase change should be as follows. Figure 5 As shown. Therefore, in order to achieve a stable beam tilt of 23° with equal spacing of 50mm, the phase difference at the center frequency should be 90 degrees, and the corresponding phase distribution needs to vary with frequency as follows: Figure 8 As shown. Through the preceding theoretical design and continuous simulation optimization, the simulated phase distribution was finally achieved. Figure 8 As shown, the overall simulated phase distribution matches the required phase distribution.

[0036] The embodiments provide radiation patterns of a one-dimensional linear array at different frequencies, such as... Figure 10 As shown, the main polarization and cross-polarization at 3.4GHz, 3.6GHz, and 3.8GHz are given in detail. The beam tilt angle at these three frequencies is essentially stable, with low cross-polarization and sidelobe levels, resulting in good overall performance and beam stability.

[0037] The examples provide the transmission phases corresponding to different baluns, such as... Figure 11As shown, different feed baluns were designed to achieve a stable 90° phase difference within the band. Due to the different equivalent circuits of the direct-feed balun and the Marchand balun, a 67° phase difference was achieved between them. When an open-circuit stub was added, it was clearly observed that the transmission phase difference changed from 67° to 90°, achieving a larger phase shift. Therefore, by adding an open-circuit stub to the direct-feed balun, a wideband transmission phase difference was achieved between it and the Marchand balun.

[0038] The example illustrates the effect of rotating the feed balun by 180 degrees on the far-field radiation phase, such as... Figure 12 As shown. Achieving a 180-degree phase shift via a fed balun is very difficult. Therefore, rotating the fed balun by 180 degrees to feed the antenna has been proposed. This method reverses the current on the dipole, thus achieving a 180-degree phasor shift in far-field radiation. Figure 12 As shown, when the feed balun is rotated 180°, a broadband 180-degree far-field radiation phase shift is achieved.

[0039] The examples illustrate the influence of different antenna shapes on the far-field radiation phase, such as... Figure 13 As shown. In Figure 12 Even after achieving a 180° phase shift, the required group delay still cannot be met. Figure 5 The group delay shown increases with increasing phase shift. However, it is difficult to achieve the corresponding group delay and phase difference simply by using a fed balun. Therefore, a larger group delay is achieved by adding a sawtooth structure and reducing the width of the dipole to change the radiation impedance and current distribution of the novel dipole. Figure 13 As shown, compared with the traditional dipole, the new dipole achieves a larger group delay and a phase distribution that better meets the requirements, with a phase error of less than 3 degrees.

[0040] The embodiments provide the overall efficiency of the one-dimensional linear array and the variation of the beam angle with frequency, such as Figure 14 As shown, the beam tilt angle variation within the band is less than 1 degree, and the overall efficiency at the center frequency is as high as 94.3%, demonstrating significant application potential.

Claims

1. A high-efficiency dual-polarized array antenna with stable beam tilt angle, characterized in that, The array antenna consists of four equally spaced different elements mounted on a metal floor. Each element consists of two parts: a planar dipole and a vertical feed balun. The four elements are ordered as follows: element 1, element 2, element 3, and element 4. The dipole structures of elements 1 and 2 are the same, as are those of elements 3 and 4. The feed balun structures of elements 1 and 3 are the same, but they are 180 degrees out of phase. The feed baluns of elements 2 and 4 are also 180 degrees out of phase. All dipoles are printed on a single PCB board with four identical square-shaped ring structures. The four ring structures form a square-shaped dipole. The feeding balun consists of two PCB boards with the same feeding structure printed on them. The two PCB boards are intersected to form a cross-shaped structure, which corresponds to the four ring structures of the dipole. The feeding balun feeds the dipole from the corner of the ring structure located at the center of the dipole.

2. The high-efficiency dual-polarized array antenna with stable beam tilt angle as described in claim 1, characterized in that, In the dipoles of the first and second units, each ring structure has a square outer shape and an internal shape. The outer and inner corners of the square ring located at the center of the dipole are chamfered.

3. The high-efficiency dual-polarized array antenna with stable beam tilt angle as described in claim 1, characterized in that, The outer shape of each ring structure in the dipole of the third and fourth units is a square; the internal shape is based on the square, with a rectangular branch extending from the midpoint of each side to the center of the square, the ends of each branch not touching, and a square branch added from each interior corner of the square; so that the interior of each ring structure is divided into five hollow areas: four hollow areas at the four corners and one hollow area in the center. The hollow areas at the four corners are axially symmetric "L-shaped", and the hollow area in the center is a square. The four corners of the hollow area in the center square are connected to the corresponding hollow areas at the four corners.

4. The high-efficiency dual-polarized array antenna with stable beam tilt angle as described in claim 1, characterized in that, The first unit's power supply balun has metal sheets printed on both sides of one of its PCB boards. The back side is printed with two vertical strips, one of which is "L"-shaped. The top of the two vertical strips is provided with rectangular protrusions to connect the corresponding dipole ring structures. The front metal sheet starts from the bottom section of the PCB board, extends upwards for a while, then bends 90 degrees to the right, then bends 90 degrees upwards again, along the projection area of ​​the "L"-shaped metal sheet on the back side to the top, then bends 90 degrees to the right again, extending to the projection area of ​​another metal sheet printed on the back side. The front metal sheet then bends downwards by 90 degrees, and the length of the branch that bends downwards by 90 degrees is less than half the length of the corresponding metal sheet on the back side.

5. The high-efficiency dual-polarized array antenna with stable beam tilt angle as described in claim 1, characterized in that, The second unit's power supply balun has metal sheets printed on both sides of one of its PCB boards. Two metal sheets are printed on the back. One of the metal sheets starts from the bottom of the PCB board, first as a horizontal rectangular sheet, then bends upwards at 90 degrees, passes through the middle of the PCB board, and then bends to the right at 90 degrees. A rectangular protrusion is set above the end of the sheet, which connects to the corresponding dipole. The other sheet includes two areas, a vertical area and a horizontal area, forming a "T" shape. The bottom of the vertical area does not exceed the middle of the PCB board, and the end of the horizontal area corresponds to the end of the first sheet on the back. The metal sheet printed on the front starts from the bottom of the PCB board, extends upwards within the projection area of ​​the first metal sheet on the back, then bends to the right at 90 degrees, then bends upwards at 90 degrees, continues along the projection area of ​​the back metal sheet to the top, then bends to the right at 90 degrees, extends to the projection area of ​​the other metal sheet printed on the back, and then splits into two paths extending upwards and downwards respectively. The upward-extending branches connect to the corresponding dipole ring structure.

6. The high-efficiency dual-polarized array antenna with stable beam tilt angle as described in claim 5, characterized in that, The fourth unit's power supply balun has a structure that adds a horizontal branch to the power supply balun of the second unit. The horizontal branch is located in the middle of the PCB board with a vertical metal sheet on the front, and extends inward.

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